1. Field of the Invention
The present invention relates to an apparatus and method for removing a shade component from an image.
2. Description of the Related Art
Recently, studies have been made to perform statistical image processing, using face images obtained by picking-up faces of persons by a camera. One example is a technique of specifying a person represented by the face image, as an application of the statistical image processing.
In the statistical image processing, a process is necessary to remove difference in conditions of image pickup from the face images as the statistical samples. Under different image pick-up conditions, light directions to one's face differ. Namely, shades appear at different portions of the picked-up face images of one same person, and hence, the one same person may possibly be erroneously recognized as a different person, when recognition is made only from the face images.
Techniques for removing shade component from face images are discussed in Japanese Patent Laying-Open Nos. 11-185025, 6-342465 and 2000-30065.
Japanese Patent Laying-Open No. 11-185025 describes a technique in which a face image is folded over at a symmetry axis of the face, and the image before folding and the image after folding are added, so as to approximate a face image that is illuminated from the front side.
Japanese Patent Laying-Open No. 6-342465 describes a technique in which a two-dimensional face image is approximated to a three-dimensional elliptical sphere, and reflected light is separated and produced from the transformed 3-dimensional face image, so as to remove the shade component.
Japanese Patent Laying-Open No. 2000-30065 describes a technique in which a set of face images of persons as the objects of recognition picked-up in advance with uniform illuminating condition are used to extract conditions other than the illumination condition, to enable recognition.
The technique described in Japanese Patent Laying-Open No. 11-185025 uses an image obtained by folding the face image on the symmetry axis. Therefore, though it is possible to remove shade from a face image picked-up under such illuminating condition in that the light comes from the left or right direction from one's face, it is impossible to remove the shade from the face image picked-up under such an illuminating condition in that light comes from the upper or lower direction or from the front or back direction.
The technique described in Japanese Patent Laying-Open No. 6-342465 involves complicated and difficult process for transforming a two-dimensional face image to a three-dimensional image of elliptical sphere. Further, as the actual face of a person is different from the elliptical sphere, shades generated at portions different from the elliptical sphere, such as the shade at one's nose, cannot be correctly separated and produced.
The technique described in Japanese Patent Laying-Open No. 2000-30065 requires preparation of face images of persons as objects of recognition by picking-up the images under the same illumination condition, which imposes severe burden.